Proximal and distal rat small intestine from control, diabetic, and insulin-treated diabetic rats was cut into strips measuring 6.0 × 10.0 mm. Strips cut along the oral-caudal axis were called longitudinal strips, while those cut 90 ° to that axis were called circular strips. The strips were stretched to their optimum lengths and subjected to electrical field stimulation (0.1-1.0-ms pulse duration, 30-270 mA, 1-26 Hz) in the presence of Krebs' solution and Krebs' solution plus 10-6 M atropine. Field stimulation produced atropine-sensitive and atropineresistant contractions in all strips. Significant differences among the three groups were found in the amplitudes of atropine-sensitive contractions in strips from distal longitudinal muscle. Controls showed the highest amplitude contractions and diabetics the lowest, whereas the insulin-treated diabetics showed contractions intermediate in amplitude. No significant differences were noted among the atropine-resistant contractions. Field stimulation delivered at pulse durations of 5.0 and 50.0 ms in the presence of neural blockade with tetrodotoxin (5 × 10-6 M) produced similar contraction amplitudes among the three groups. These results suggest that streptozotocin-induced diabetes mellitus is associated with defective cholinergic neuromuscular transmission in the myenteric plexus of the distal small intestine. Insulin therapy seems to improve the abnormality.
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